Thermionic valve circuit arrangement



Patented Dec. 23, 1941 MEN John Hardwick, West Drayton, England, assignor to Electric & Musical Industries Limited, Hayes, Middlesex, England, a company of Great Britain Application May 18, 1940, Serial No. 335,896 In Great Britain March 9, 1939 2 Claims.

This inlvention relates to thermionic valve circuit arrangements and has particular reference to the decoupling arrangements employed in circuits operating at high frequencies.

Owing to the relatively large physical dimensions of the decoupling condensers usually employed, it is inconvenient to mount them as close as is desirable to the amplifier valves whose anode circuits are to be decoupled and the condensers are therefore mounted in positions which are convenient from the point of view of constructional assembly. The use of undesirably long connecting leads is thus involved with consequential detrimental effects upon the frequency response characteristic of the amplifier. In order to overcome irregularities in the frequency curve of the amplifier, it may be necessary to insert a compensating network comprising resistance, capacity and inductance in the anode circuit of the valves. Calculations have to be made in order to ascertain the values required for such compensating components and tests made over a range of frequencies in order to ascertain whether the required compensation has been effected.

The object of the present invention is to provide a decoupling arrangement which enables the constructional advantages of assembly of a decoupling condenser remote from its associated valve to be retained, without involving provision of the compensating means referred to.

According to the present invention thermionic apparatus includes a thermionic valve and means for decoupling an electrode of said thermionic valve, said decoupling means comprising in combination a decoupling condenser and a screened conductor, said screened conductor comprising an inner conductor and an outer conducting sheath, said electrode being connected to one terminal of said condenser by said inner conductor and said outer conducting sheath being connected at one end to the other terminal of said condenser and at its other end to earth. The decoupling means described may with particular advantage be employed for decoupling the anode electrodes of the valves. The end of the sheath at the condenser may be arranged to shield the condenser terminals to which the inner conductor is connected.

While it will be understood that the invention may be applied to any thermionic valve apparatus including decoupling condensers for the valves, one particular application of theinvention is disclosed by way of example in the accom- 'panying drawing and will be described hereinafter in greater detail. Thus,'in the case of a high frequency amplifying panel having a number of valves (only one of which is shown) and associated components assembled compactly in a metal screening box, the anode decoupling condensers which may have capacities of four microfarads and are therefore too large to permit easy assembly close to the associated valves are mounted in a position which is convenient from the point of view of mechanical assembly. The valve I is provided with the usual cathode 2, grid 3 and anode 4. Connected between the anode and the source H. T. of positive potential are the anode resistance 5 and decoupling resistance 6. The anode of each of the valves to be decoupled is connected to its decoupling condenser 1 by a screened conductor 8-9, the shielded inner conductor 8 being connected at one end to the anode to be decoupled, and at the other end to one terminal 1' of the condenser. The outer sheath 9 of the screened conductor is connected at one end to the other terminal I of the condenser and the other end of the sheath is connected through the connection ID to the earthed metal box containing the components.

By connecting the anodes of the valves to the decoupling condensers in the manner indicated it is found that a substantially uniform frequency response curve is obtained. It will, of course, be understood that decoupling condensers for other electrodes of the valves such as the screening grids, where screen grid valves are employed, may be similarly connected.

The invention is also applicable to the bypassed condenser associated with the cathode biasing resistor where it is desired or found necessary to locate such condenser at a convenient distance from the valve. As shown in the drawing the cathode end of the resistor II is connected to one terminal of the by-pass condenser l2 by means of the shielded inner conductor l3. The outer sheath [4 of the shielded conductor has one end connected to the grounded side of the resistor H and the other end connected to the other terminal of the by-pass condenser.

I claim:

1. 'I'hermionic valve apparatus comprising a thermionic valve and means for decoupling the anode of said thermionic valve, said decoupling means comprising in combination a decoupling resistor included in the anode circuit and in close proximity to the valve, a decoupling condenser which by reason of its relatively large physical dimensions is mounted at a point remote from the valve and decoupling resistor, and a screened conductor, said screened conductor comprising an inner conductor and an outer conducting sheath, the anode end of the decoupling resistor being connected to one terminal of said condenser by said inner conductor and said outer conducting sheath being connected at one end to the other terminal of said condenser-and at its other end to earth.

2. Thermionic valve apparatus according to claim 1 wherein the end of said outer conducting sheath extends for a suflicient distance beyond the inner conductor to shield the condenser terminal to which said inner conductor is connected.

JOHN HARDW'ICK. 

